You also should check out the News Rover program that automatically scans Usenet newsgroups, downloads messages of interest to you, decodes binary file attachments, reconstructs files split across multiple messages, and eliminates spam and duplicate files.

Fit A Four-Parameter Logistic Function

The following NLREG program fits a 4-parameter logistic (sigmoidal) function to model heart rate as a function of blood pressure.

The five parameters that define the function are:
P1 = second plateau
P2 = range of response. Note: (P1+P2) gives the first plateau
P3 = curvature parameter
P4 = value at inflection point